1FFS(3)                     Linux Programmer's Manual                    FFS(3)
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NAME

6       ffs, ffsl, ffsll - find first bit set in a word
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SYNOPSIS

9       #include <strings.h>
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11       int ffs(int i);
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13       #include <string.h>
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15       int ffsl(long int i);
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17       int ffsll(long long int i);
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19   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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21       ffs():
22           Since glibc 2.12:
23               _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 200809L ||
24               _XOPEN_SOURCE >= 700 ||
25           Before glibc 2.12:
26               none
27       ffsl(), ffsll():
28           _GNU_SOURCE
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DESCRIPTION

31       The ffs() function returns the position of the  first  (least  signifi‐
32       cant)  bit  set in the word i.  The least significant bit is position 1
33       and the most significant position is, for example, 32 or 64.  The func‐
34       tions  ffsll()  and  ffsl()  do the same but take arguments of possibly
35       different size.
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RETURN VALUE

38       These functions return the position of the first bit set, or  0  if  no
39       bits are set in i.
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CONFORMING TO

42       ffs(): 4.3BSD, POSIX.1-2001.
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44       The ffsl() and ffsll() functions are glibc extensions.
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NOTES

47       BSD systems have a prototype in <string.h>.
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SEE ALSO

50       memchr(3)
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COLOPHON

53       This  page  is  part of release 3.53 of the Linux man-pages project.  A
54       description of the project, and information about reporting  bugs,  can
55       be found at http://www.kernel.org/doc/man-pages/.
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59GNU                               2010-09-20                            FFS(3)